Combustion process with selective heating of combustion and quench air

ABSTRACT

A new combustion process wherein combustion efficiency is retained while reducing inlet air temperature to the combustor so as to obtain reduced nitrogen oxides emissions. A new combustor, and a new combination of combustion apparatus and heat utilization apparatus are also provided.

United States Patent 1191 Q g 1 1 July 30, 1974 [54] COMBUSTION PROCESSWITH SELECTIVE 3,705,492 12/1972 Vickers 60/3951 R HEATING OF COMBUSTIONAND UENCH AIR Q FOREIGN PATENTS OR APPLICATIONS Inventor: Harold Quigg,art1esvi11 586,602 3/1947 Great Bmain 60/39.5l [73] Assignee: PhillipsPetroleum Company, OTHER PUBLICATIONS Bartlesvlne Okla' EngineeringKnowhow in Engine Design part 19, Sae Flled! 1972 Publication SP 365PIS-010922, pg. 7. [21] Appl. N0.: 238,318 Related Application a IPrimary Examiner-Carlton R. Croyle [63] Continuation-in-part of Ser. No.208,245, Dec. 15, Assistant Exqmmer warren Olsen 1971, abandoned. v i 52us. (:1 60/39.02, 60/3906, 60/3951, [571 ABSTRACT 51 t Cl 6 3 A newcombustion process wherein combustion effld O6 g 51 cienc-y is retainedwhile reducing inlet air temperature 1 o arc 2 to the combustor so as toobtain reduced nitrogen oxides emissions. A new combustor, and a newcombination of combustion apparatus and heat utilization ap- [56]References and paratus are also provided. I UNITED STATES PATENTS 13,608,309 9/1971 Hill et al..; 60/3965 22 Claims, 12 Drawing Figures(EXHAUST 27 24 HEAT EXCHAN CC ZONE SIZ I I COMBUSTOR AIR'\ 10- FUEL-| 16I L I8 I A A fTUR-BINE LOAD COMPRESSOR -25 PATENTEDJULSOIHH SHEEI t 0F 4JmDu COMBUSTION PROCESS WITH SELECTIVE HEATING O COMBUSTION AND UEN I AR This application is a continuation-in-part of copending applicationSer. No. 208,245, filed Dec. 15, 1971, now abandoned.

This invention relates to improved combustion processes, improvedcombustors which can be employed in said processes, and an improvedcombination of combustion apparatus and heat utilization apparatus.

Air pollution has become a major problem in the i United States andother highly industrialized countries of the world. Consequently, thecontrol and/or reduction of said pollution has become the object ofmajor research and development effort by both governmental andnongovernmental agencies. Combustion of fossil fuel is a primary sourceof said pollution. it has been alleged, and there is supportingevidence, that the automobiles employing conventional piston-typeengines burning hydrocarbon fuels are a major contributor to saidpollution. Vehicle emission standards have been set by the United StatesEnvironmental Protection Agency which are sufficiently restrictive tocause automobile manufacturers to consider employing alternate enginesinstead of the conventional piston engine.

The gas turbine engine is being given serious consideration as analternate engine. However, insofar as is presently known, there is nopublished information disclosing realistic and/or practical combustionprocesses or combustors which can be operated at conditions typical ofthose existing in high performance engines, and which will have emissionlevels meeting or reasonably approaching the standard set by said UnitedStates Environmental Protection Agency. This is particularly true withrespect to nitrogen oxides emissions. Thus, there is a need for acombustion process, and a combustor of practical and/or realisticdesign, which can be operated in a manner such that the emissionstherefrom will meet said standards. Even a process and/or a combustorgiving reduced emissions approaching said standards would be a greatadvance in the art. Such a process or combustor would have greatpotential value because it is possible the presently very restrictivestandards may be reduced.

In the operation of combustion processes, conservation of the thermalenergy produced is essential for efficiency. For example, in current gasturbine engines being proposed for automotive service, the turbineexhaust gases are heat exchanged with the inlet air to the primarycombustion zone of the combustor so as to recover heat from said exhaustgases and improve overall efficiency. However, these engines will notmeet the emission standards set by said Environmental Protection Agency.

The present invention solves the above-described problems byheatexchanging the turbine exhaust gases with another air stream to thecombustor, e.g., the dilution or quench air, instead of the primaryinlet air. The method of the invention thus provides for reducing thetemperature of the primary inlet air to the combustor. This reduces thetemperature in the combustor which results in reduced nitrogen oxidesemissions. Thus, the overall advantageous result of the inventionincludes (1) reduction of nitrogen oxide emissions from the combustorwhile (2) maintaining thermal efficiency by returning the recovered heatto the process at a point where it has no effect on nitrogen oxidesproduction. The invention also provides novel combustors, and a novelcombination of combustion apparatus and heat utilization apparatus.

Thus, according to the invention there is provided in a method wherein astream of air and a stream of fuel are passed to a combustion zone, atleast partially mixed to form a combustible mixture which is burned toproduce hot combustion gases containing heat energy, and said hotcombustion gases are passed to a heat energy utilization zone to utilizea portion of said heat energy, the improvement comprising: dividing saidstream of air into a first stream of air and a second stream of air;passing at least a portion of said first stream of air to saidcombustion zone; passing said second stre/am of air in heat exchangerelationship with an exhaust stream from said heat energy utilizationzone to heat said second stream of air and thereby utilize an additionalportion of said energy; and passing at least a portion of said heatedsecond stream of air into a quench region of said combustion zone.

Further according to the invention, there is provided an apparatus forproducing and utilizing heat energy,

comprising, in combination: an'air supply conduit; a

combustion means for burning a fuel to produce hot combustion gasescontaining heat energy; a fuel inlet means for introducing a fuel intosaid combustion means; a primary air conduit means connected to said airsupply conduit and said combustion means for introducing a stream of aircomprising primary air into said combustion means; a heat exchangemeans; a quench air conduit means connected to said air supply conduit,said heat exchange means, and said combustion means for delivering astream of air comprising quench air from said air supply conduit,through said heat exchange means, and into said combustion means; a heatenergy utilization means for utilizing a portion of said heat energy; aneffluent conduit means for passing said hot combustion gases from saidcombustion means to said heat energy utilization means; and an exhaustconduit means connecting said heat energy utilization means and saidheat exchange means for passing said hot combustion gases from said heatutilization means and into heat exchange relationship with said streamof quench air to heat said quench air and thereby utilize an additionalportion of said heat en- Still further according to the invention, thereis provided a combustor comprising, in combination: an outer tubularcasing; a flame tube disposed concentrically within said casing andspaced apart therefrom to form a first annular chamber between saidflame tube and said casing; an air inlet means for introducing a stream.of air comprising primary air into the upstream end portion of saidflame tube; a fuel inlet means for introducing fuel into the upstreamend portion of said flame tube; an imperforate sleeve surrounding anupstream portion of said flame tube and spaced apart therefrom tolongitudinally enclose an upstream portion of said first annular chamberand define a second annular chamber between said sleeve and said outercasing; a wall member closing the downstream end of said secondannularchamber; a baffle member closing the upstream end of said enclosedportion of said first annular chamber; at least one opening provided inthe wall of said flame tube at a first station located intermediate theupstream and downstream ends thereof; a first conduit means extendingfrom said second annular chamber into communication with said openinglocated at said first station for admitting a second stream of air fromsaid second annular chamber into the interior of said flame tube; atleast one other opening prolocated downstream from said first stationfor admitting a third stream of air from said first annular chamber intothe interior of said flame tube; and a second conduit means extendingthrough said outer casing, said second annular chamber, said sleeve, andinto communication with said enclosed portion of said first annularchamber for admitting a stream of air thereto.

FIG. 1 is a diagrammatic flow sheet illustrating methods of producingand utilizing heat energy in accordance with the invention.

FIG. 2 is a diagrammatic illustration of methods and apparatus inaccordance with the invention.

FIG. 3 is a view in cross section of a combustor in accordance with theinvention.

FIG. 4, 5, 6, and 7 are views in cross section taken along the lines4-4, 5-5, 6-6, and 77, respectively, of FIG. 3.

FIG. 8 is a fragmentary perspective view of a combustor flame tubeillustrating another type of fin or extended surface which can beemployed thereon.

FIG. 9 is a partial view in cross section of another combustor inaccordance with the invention.

FIG. 10 is a front elevation view taken along the lines 10-10 of FIG. 9.

FIG. 11 is a cross section view in elevation of the swirl plate of thedome or closure member in the combustor of FIG. 9.

FIG. 12 is a diagrammatic view, partially in cross section of anothercombustor in accordance with the invention.

Referring now to the drawings, wherein like reference numerals areemployed to denote like elements, the invention will be more fullyexplained. In FIG. 1 a stream of air from an air supply conduit 10 isdivided into a first stream of air in conduit 12 and a second stream ofair in conduit 14. In one embodiment, at least a portion of said firststream of air 12 is passed into combustion zone 16. A stream of fuel isintroduced into said combustion zone via conduit 18. Said combustionzone can comprise any suitable type of combustion zone for burning amixture of fuel and air to produce hot combustion gases containing heatenergy. For example, said combustion zone can be a combustor in a gasturbine engine, a combustor in an aircraft jet engine, a combustor orother furnace employed in a boiler for generating steam, or other typesof stationary power plant, etc.

Said fuel and said first stream of air are at least partially mixed toform a combustible mixture which is burned to produce hot combustiongases containing heat energy. Said hot combustion gases are passed viaconduit to heat energy utilization zone 22 so as to utilize a portion ofthe heat energy in said gases. Said heat energy utilization zone cancomprise any suitable method and/or means for utilizing or putting touse the heat energy contained in said hot combustion gases. For example,a turbine in a gas turbine engine wherein heat energy is converted tomechanical energy, or the heat exchange tubes in a boiler where water isconnected to steam, etc.

Said second stream of air in conduit 14 is passed through heat exchangezone 24 in heat exchange relationship with an exhaust stream in conduit26 from heat energy utilization zone 22 so as to heat said air andthereby utilize an additional portion of said heat energy. Said heatexchange zone can comprise any suitable method and/or means foreffecting heat exchange between two separate streams of fluids, e.g.,indirect heat exchange. The heated second stream of air is passed fromsaid heat exchange zone via conduit 15 and returned to said combustionzone 16, preferably at a downstream location therein, to serve as adiluent or quench medium to lower the temperature of the effluent gasesin conduit 20 before they are passed to the heat energy utilization zone22.

In one preferred embodiment of the invention, said combustion zone 16can comprise a primary combustion region, a secondary combustion regionlocated downstream from said primary combustion region, and a quench ordilution region located downstream from said secondary combustionregion. In this and other embodiments, said first stream of air inconduit 12 is further divided into a stream comprising primary air andanother stream comprising secondary air. Said primary air is introducedinto said primary combustion region and said secondary air is introducedinto said secondary region via conduit 30. At least a portion of saidheated second stream of air is introduced into said quench or dilutionregion via conduit 15, as before.

In another preferred embodiment of the invention, a portion of saidheated second stream of air in conduit 15 can be passed via conduit 31into conduit 30 for mixing with and increasing the temperature of thesecondary air therein. The valves in said conduits 30 and 31 can beemployed to regulate the relative proportions of the two streams of air.

FIG. 2 illustrates one embodiment of the invention wherein the effluentgases from combustor 16 are passed via conduit 20 to a turbine 25. Inturbine 25 a portion of the heat energy in said gases is converted tomechanical energy to drive shaft 28 which can be connected to anysuitable load. Exhaust gases from turbine 25 are passed via conduit 26to heat exchanger 24 and exhausted therefrom via conduit 27.

In FIG. 3 there is illustrated a combustor in accordance with theinvention, denoted generally by the reference numeral 40, whichcomprises an elongated flame tube 42. Said flame tube 42 is open at itsdownstream end, as shown, for communication with a conduit leading to aturbine or other utilization of the combustion gases. A closure or domemember, designated generally by the reference numeral 44, is providedfor closing the upstream end of said flame tube, except for the openingsin said dome member. An outer housing or casing 46 is disposedconcentrically around said flame tube 42 and spaced apart therefrom toform a first annular chamber 48 around said flame tube and said dome orclosure member 44. Said annular chamber 48 is closed at its downstreamend by any suitable means such as that illustrated. Suitable flangemembers, as illustrated, are provided at the downstream end of saidflame tube 42 and outer housing 46 for mounting same and connecting sameto a conduit leading to a turbine or other utilization of the combustiongases from the combustor. Similarly, suitable flange members 50 and 52are provided at the upstream end of said flame tube 42 and said outerhousing 46 for mounting same and connecting same to a suitable conduitmeans which leads from a compressor or other source of air. Asillustrated in the drawing, said upstream flange members comprise aportion of said outer housing or casing 46 which encloses dome member 44and forms the upstream end portion of said first annular chamber 48. Itwill be understood that outer housing or casing 46 can be extended, ifdesired, to enclose dome 44 and said upstream flanges then relocated onthe upstream end thereof. While not shown in the drawing, it will beunderstood" that suitable support members are employed forsupporting-said flame tube 42 and said closure member 44 in the outerhousing 46 and said flange members. Said supporting members have beenomitted so as to simplify the drawing.

An air inlet means is provided for introducing a swirling mass or streamof air into the upstream end portion of flame tube 42. As illustrated inFIGS. 3 and 6, said air inlet means comprises a generally cylindricalswirl chamber 54 formed in said dome member 44. The downstream end 'ofswirl chamber 54 is in open communication with the upstream end of flametube 42. A; plurality of air conduits 56 extend from said first annularchamber 48, or other suitable source of air, into, swirl chamber 54tangentially with respect to the inner? wall thereof.

A fuel inlet means is provided for introducing a stream of fuel into theupstream end portion of flame tube 42. As illustrated in FIG. 3, saidfuel inlet. means comprises a hollow conduit 58 for introducing a streamof fuel into the upstream end of swirl chamber 54 and;

axially with respect to said swirling stream of air. Any other suitablefuel inlet'means can be employed.

A flared expansion passageway 60 is formed in the downstream end portionof dome or closure member 44. Saidflared passageway flares outwardlyfrom the downstream end of swirl chamber 54 to a point on the inner wallof flame tube 42. 4

An imperforate sleeve 62 surrounds an upstream portion of said flametube 42. The outer wall of said sleeve; can be insulated, if desired andthus increase its effectiveness'as a heat shield. Said sleeve 62 isspaced apartfrom flame tube 42.so as to longitudinally enclose anupstream portion 48 of said first annular chamber 48 and define a secondannular chamber 64 between said sleeve 62 and outer casing 46. Anannular wall member 66, secured to the inner periphery of casing 46, ispro-l vided for closing'the downstream end of said second annularchamber 64. An annular baffle member 68, secured to the outer wall offlame tube 42 and the inner wall of sleeve 62, is provided for closingthe upstream end of said enclosed portion 48' of first annular space 48.At least one opening is provided in the wall of. flame tube 42 at afirst station located intermediate the ends of said flame tube. In mostinstances, it will be preferred to provide a plurality of openings 70,as illus trated. A generally tubular conduit means 72 extends; from saidsecond annular chamber 64 into communica-- tion with said opening 70 foradmitting a second stream of air from said second annular chamber 64into the in-v terior of flame tube 42. When a plurality of openings, 70are provided, a plurality of said tubular conduits 72- are alsoprovided, with each individual conduit 72; being individually connectedto an individual opening? 70. The above-described structure thusprovides an imperforate conduit means comprising second annular chamber64 andtubularconduius) 72 for admitting a second stream ofair into theinterior of flame tube 42. ,r At least one other opening 74 is providedin the wall:

of flame tube 42 at a second station located down-;

stream and spaced apart from said first station for admitting a thirdstream of air from first annular chamber; 48 into the interior of flametube 42. In most instances,

' it will be preferred to provide a plurality of openings 74 and 78 canbe arranged in rows which extend around the periphery of the flame tube42,.andwhich are spaced apart longitudinally on-said flame tube. Thefins or tabs 76, in each row thereof, can be spaced apartcircumferentially to provide passageways 77 therebetween. See FIG. 4.Similarly, passageways 79 can be provided between the circumferentiallyspaced apart fins or tabs 42. See FIG. 5. FIG. 8 illustrates anothertype of fin which can be employed. In FIG. 8 the fins 80 extendlongitudinally of flametube 42. Said fins 76,

78, and 80 can extend into enclosed portion 48' any desired distance. j

FIG. 7 illustrates one type of structure, which can be employed toprovide tubular conduits 72'. A plurality of boss members 82, spacedapart circumferentially in a rowaround the periphery of flame tube 42,is provided downstream from the last row of fins 78. Said boss members82 havethe general shape of fins 76 and 78 and'passageways 83 areprovided therebetweemsimilarly as for passageways 77 and 79 in the rowsof fins I 76 and 78. Said imperforate sleeve62 extends over boss members82, similarly as for fins 76 and 78, and

said conduits 72 can be formed by cutting through said 'sleeve 62 andsaid boss members 80 into communication with openings 70 in flame tube42. Said passage ways 77, 79 and 83 thus provide communication throughenclosed portion 48, around tubular conduits 72, and into the downstreamportion of first annular chamber 48.

g a fuel conduit 92 leading from a source of fuel, commuh I v chamber64, said sleeve 62, and into communication Referring now to FIG. 9,there is illustrated the upstream portion of another combustor inaccordance with the invention. The downstream portion of the combustorof FIG. 9 is like the combustor of FIG. 3. A closure member or dome,designated generally by the reference numeral 85, is mounted inthe-upstream end of flame tube 42 so as to close the upstream end ofsaid flame tube except for the openings'provided in said closure member.Said closure member can befabricated integrally, i.e., as one element.However, in most instances it will be preferred to fabricate saidclosure member in a plurality of pieces, e.g., an upstream element86, aswirl plate 87 (see FIG. 11), and a downstream element or radiationshield 88. An air inlet '10, and 11, said air inlet means comprises aplurality of air conduits 90 and 90' extending through said upstreammember 86 and said swirl plate 87, respectively.

A plurality of angularly disposed baffles 91, one for each of said airconduits 90, are formed on the downstream side of said swirl plateadjacent the outlets of said air conduits.

A fuel inlet means is provided for introducing a stream of fuel into theupstream end of flame tube 42. As illustrated in FIG. 9, said fuel inletmeans comprises nicating with a passageway 93 formed in upstream eleasatifi his in m a ni lqa satesx tlt smbsr s4;'sisamaieaaeieihem's6; Aspray nozzle 95 is.

mounted in a suitable opening in the downstream side of said element 86and is in communication with said chamber 94. Any other suitable type ofspray nozzle and fuel inlet means can be employed, including other airassist atomization nozzles. For example, it is within the scope of theinvention to employ other nozzle types for atomizing normally liquidfuels such as nozzles wherein a stream of air is passed through thealong with the fuel.

FIG. 12 is a diagrammatic illustration of another type of combustorwhich can be employed in the practice of the inventiQmThis combustor issimilar to the combustor illustrated in FIG..3. In the combustor of FIG.12

the tubular conduits 72' extend transversely throughv In a preferredmethod of operating the combustor of FIG. 3, a stream of air from acompressor or other source (not shown) is divided into a first stream ofair and a second stream of air, said first stream of air'is passed, viaa conduit connected to flange 52, into the? upstream end of annularspace 48. Said first stream of air is further divided into a streamcomprising primary air and a stream comprising secondary air. Saidprimary air-is passed from annular space 48, through tangential conduits56, and into swirl chamber 54. Said tangentialconduits impart a helicalor swirling motion to the airentering said swirl chamber and exitingtherefrom. This swirling motion creates a strong vortex action resultingin a reverse circulation of hot gases within flame tube 42.

A stream of fuel, preferably prevaporized, is admitted, via conduit 58,axially of said swirling stream of air. Controlled mixing of said fueland said air occurs at the interface therebetween. The fuel and air exitfrom swirl chamber 54 via expansion passageway 60 wherein they areexpanded in a uniform and graduated manner, d ur-.

ing at least a portion of the mixing thereof, from the volume in theregion of the initial contact therebetween to the volume of the primarycombustion region, i.e., the upstream portion of flame tube 42.

Said secondary air is passed from the upstream end of annular chamber 48via second annular chamber 64,-,

tubular conduits 72, and openings 70 into a second region of thecombustor which is located downstream from said primary combustionregion.

The above-mentioned second stream of air, after via openings 74 into athird region of the combustor which is located downstream from saidsecond region. Said second stream of air comprises and-can be referredto as quench or dilution air. Conduit 15 can communicate with enclosedportion 48', 'or the downstream portion of first annular space orchamber 48, at any desired location. However, the upstream end ofennozzle 8 closed portion 48' is a preferredlocatidfbi ause theair'flowing over the finned wall portion of flame tube 42 serves to coolsaid wall portion and remove heat from the interior of said flame tube,and thus cause the primary combustion region to operate at a lowertemperature. This'aids further in reducing nitrogen oxide emissions. I

In one preferred method, the operation of the combustor of FIG. 9 issimilar to the above-described operation of the combustor of FIG. 3, andreference is made thereto. The principal difference is in the operationof closure member (FIG. 9) and closure member 44 (FIG. 3). In FIG. 9,primary air is passed through said :openings and 90, strikes saidbaffles 91, and has a swirlingmotion imparted thereto in chamber 89. Aswirling stream of air exits from swirl chamber 89 1 through the openingin radiation shield 88 which surrounds nozzle 95. A stream of liquidfuel is passed through conduit 92, passageway 93, chamber 94, and exitsfrom nozzle in a generally cone-shaped discharge. Said fuel contactssaid stream of air, with said air stream assisting the action of nozzle95 in atomizing said fuel.

The'operation of the combustor illustrated in FIG. 12

,is similar to that described above for the combustors of FIGS. 3 and 9,taking into consideration the type of dome or closure member employed onthe upstream ends of the flame tubes. The combustor of FIG. 12 isparticularly adapted to be employed in those embodimerits of theinvention wherein the stream of secondary air admitted through openings70 can have a temperature greater than the temperature of the primaryair ad mitted through dome orclosure member 44. When tubular conduits 72are connected to the same source of air as is supplying chamber 48, thetemperature of the secondary air can be substantially the same as theprimary air. Or, the temperature of the secondary air can be increasedto be greater than the temperature of the primary air by means of aconnection between said combustors or combustion zones employed in thepractice of the invention under any conditions which will give theimproved results of the invention. For example, it is within the scopeof the invention to operate said combustors or combustion zones atpressures within the range of from "about I to about 40 atmospheres, orhigher; at flow velocities withinthe range of from about 1 to about 500feet per second, or higher; and at heat input rates within the range offrom about 30 to about 1,200 Btu per pound of air. Since the inventionprovides for reducing the temperature of the primary inlet air to thecombustor or combustion zone, to values less than those normallyemployed, so as to reduce'nitrogen oxides emissions, it is preferredthat the temperature of the inlet primary air be within the range offrom ambient to about 700 F., more preferably from ambient to about 500F. In a preferred em- However, it is within the scope of the inventionfor the temperature of the secondary air to be greater, e.g.,

l carbon was measured by the technique described by Lee and Wimmer, SAEPaper 680769. Each pollutant measured is reported in terms of pounds per1,000 pounds of fuel fed to the combustor. The results of flame tubewall or is heated by having a portion of the th r ns wer as followheated air in conduit 15 mixed therewith via conduit 31, see FIGS. 1 and2. The temperature of the dilution Test Conditions or quench air can beany suitable temperature depend- Combustor operating variames Idle Poweri ing upon materials of construction in the equipment T 900 1100employed downstream from the combustor, e.g., turg' f f a g 50 HO bmeblades, and. how much it is desired to cool the Velocity, Cold Flow,ft./sec. 250 250 combustor effluent. Generally speaking, operating co'n-Heat Rate' 200'. ditions in the combustors employed in the practice ofEmissi ns, l s 10001115, Omar the invention will depend upon where thecombustor is employed. For example, when the combustor is emggggg'hgf gfz ,3' 8 ployed with a high pressure turbine, higher pressuresHydrocarbons 0.6 0.2

and higher inlet air temperatures will be employed in the combustor.Thus, the invention is not limited to any particular operatingconditions.

In another series of runs wherein the combustor was operated (using thesame fuel) at a pressure of 450 The relative volumes of theabove-described primary; iinches of Hg..abs., a gas velocity of 140 feetper second,

secondary, and quench or dilution air streams will depend upon the otheroperating conditions. Generally speaking, the combined volume of saidprimary air and said secondary air will usually be a minor proportion ofthe total air to the combustor, e.g., less than about 50 volume percent,with" said primary air being in the range of up to about volume percentand said secondary air being in the range of up to about 24 volumepercent. The volume of said quench or dilution air will usually be amajor portion of the total air to the combustor, e.g., more than about50 volume percent. The relative volumes of said primary, secondary, andquench air streams can be controlled by varying the sizes of theopenings, relative to each other, through which said streams of air areadmitted to the flame tube. Any other suitable meansof controlling saidair volumes can be employed, e. g., flow meters on each air stream.

The term air is employed generically herein and in the claims, forconvenience, to include air and other combustion-supporting gases.

The following examples will serve to further illustrate the invention.

EXAMPLE I A series of runs was made in a combustor typical of? prior artcombustors. Said combustor basically embodied the princill features ofcombustors employed in,

modern aircraft turbine engines. The combustor was a; straight-throughcan-type combustor employing fuel atomization by a single simplex-typenozzle. The combustor liner (flame tube) was fabricated from 2-inch'pipe, with added internal deflector skirts for air film; cooling ofsurfaces exposed to the flame. Exhaust emis-f sions from this combustor,when operated at comparable conditions for combustion, are in generalagree-i ment with measurements presently'available from scv-i eraldifferent gas turbine engines. A commercial Typei A jet fuel wasemployed in these test runs. Runs were made at operating conditionssimulating idle conditions; and at operating conditions simulatingmaximum; power conditions. Analyses for content of nitrogen oxides(reported as NO), carbon monoxide, and hydro-, carbons (reported ascarbon) in-the combustor exhaust! gases were made at each testcondition. The method for measuring nitrogen oxides was based on theSaltzman ;;and a variable heat input rate, it was found that when theair inlet temperature was increased over a range from 400 F. to aboutl,l50 F., the nitrogen oxides emissions increased substantiallyuniformly from about ,3 to about 23.5 lbs. per 1,000 lbs. of fuelburned.

Based on the above data, it was calculated that a "combustor orcombustion zone operated in accordance with the method of the invention,at a primary air inlet temperature of about 300 F., would have nitrogenoxides emissions of about 0.6 pound per 1,000 pounds of fuel at idleconditions, and about 09 pound per 1,000 pounds of fuel at maximum powerconditions.

EXAMPLE H Y A series of test runs was carried out employing com bustorsA and B. Combustor A was like the combustor illustrated in FIG. 3 exceptthat conduit 15 was omitted and a row of fins 76 replaced baffle 68.Combustor B was like the combustor illustrated in FIG. 9 except thatconduit 15 was omitted and a row of fins 76 replaced baffle 68.Additionally, the fins on the flame tube of combustor B were modified byplacing l/8 inch bars longitudinally through each row of fins 76 andeach row of fins 78. This provided a more linear path h hst slq sdassafir s details of a t bustors-are set forth in Table 11 below. Saidcombustors and the design details thereof are here used for illustrativepurposes only and the invention is not to be coni strued as limitedthereto. Any suitable combustor having any suitable dimensions can beemployed in the practice of the invention. In these runs the heat input(fuel flow) was varied, with the air flow remaining fixed, at differentcombinations of combustor pressure, reference velocity, and inlet airtemperature. Combustor A was run using a prevaporized fuel. Combustor Bwas run using a liquid atomized fuel. Properties of the fuel used inboth combustors are setforth in Table 1 below.

The method of operation was the same for bothcombustors. For example,referring to FIG. 3, a stream of air from a compressor was passed intothe upstream end of annular space 48 and there divided. A portion ofsaid air was passed as primary air via inlet conduits 56 into theprimary combustion region of the combustor. -A second portion of saidair was passed as secontechnique, Analytical Chemistry 26, No. 12, 1954,pages l,949-l,955. Carbon monoxide was measured by a conventionalchromatographic technique. Hydrothe combustorfi third portion of saidair was passed dary air via annular chamber 64 tubular conduits 72, andopenings into a secondary combustion region of portion ofafiFuEiF'EFafiiBer 4'8; iidbp h'i ggm into PHYSICAL AND CHEMICALPROPERTIES OF TEST FUEI. the quench region of the combustor. Like flowswere a used in the combustor illustrated in FIG. 9. Using said flows,each of said combustors was operated at the test vummw I M d V A 0points or conditions set forth in Table III below. Analyrm l d) (Cu n)ses for emissions content in the combustor exhaust smichiomemc Fuel/AirRatio Mm 0.0676

gases were carried out as in Example I. Emissions data .for saidtestruns, mean values from duplicate runs at each test condition, areset forth in Tables IV and V be- TA BLE II v COMBUSTOR DESIGN low. v

. Combustor Number Variable A B TABLE I Closure Member 0 875 p t h .6

PHYSICAL AND CHEMICAL PROPERTIES OF TEST FUEL f i f g es Tangent 3 HoleDiameter, inches 0.188 0.250

Philjet A-50 Number of Holes 6 6 Total Hole Area, square inches 0.1660.295

ASTM Distillation F Total Combustor Hole Area 3.213 S 5.5171

Initial Boiling Point 340 gyfi l f ib eg fgggfi g Fuel Tube Diaineter,inches 0.250

20 vol. evaporated I 371 Fl 1 vol. evaporated 376 1232:55

' VOL evaporated 387 25 Hole Diameter, inches 5/16X1* 5/15X1 evaporated398 I v Total Number of Holes a s vol. evaporated 409 Total l-Iole Area,square inches 2.500 2.500 vol. evaporated 424 Total Combustor Hole Area48.393 47.214 vol. evaporated 442 Second-Station vol. evaporated 461 IHole Diameter, inches 5/16Xl 5/l6Xl" vol. evaporated 474 Total Number ofHoles 8 8 End Point I 496 Total Hole Area, square inches 2.500 2.500Residue, VOL p 03 30 %.Total Combustor Hole Area 48.393 47.214 Loss,vol. 0.0

Gravity, degrees API 46.6 'gl gglgustor Cross-Section Area, square 3.3553.355

Density, lbs/gal. v 6.615 I Heat of Combustion. net, Btu/lb. 18,670 'lgg Hole Area Square 5'295 I Hydrogen Content. I Cross-Sectional Area153.933 157.777

Smoke Point. mm 27.2 35 I Sulfur. w 01101 .Combustorlnside Diameter,inches 2.067 2.067

Gum, mg/ ml 1 0. Primary Zone Length, inches 7.375 7.375

Composition, vol. Volume, cubic inches 7 24.748 24.748 Paraffins 52-Combustor Length, inches 18.437 18.437 Cycloparaffins 34.5 Volume, cubicinches 61.867 61.867 Olefins 0.1 v Aromatics 12.6 "Holes are 5/16 inchdiameter at ends; slots are 1 inch long.

TABLE III TEST CONDITIONS COMBUSTORS A 8L B Test Condition Primary InletAir Combustor Cold Flow Heat Input, Btu/lb. Air Flow plbJsec. Fuel Flow,lb./hr.

Number Tempcraturc, F. Pressure, in Hg. Reference Air I a Vclocity,ft./sec.

1 1100 I10 I 250 75 0.545 '75) 2 do. do. do. do. 11.6 3 do. do. do. do.15.8 4 do. I dol do. do. 19.4 5 do. do. do. 225 do. 236 6 do. do. do.260 do. 27.3 7 do. do. do. I 300 do.- 31.5

I s 900 110 250 75 0.625 9.0 9 do. do. do. 110 do. 13.3 10 do. do. do.150 do. 18.1 11 do. do. do. 185 I do. 22.3 12 do. do. do. 225 do. 27.113 do. do. do. 260 do. 31.3 14 do. do. do. 300 do. 36.2

15 700 110 I 250 75 0 733 10.6 16 do do do. 110 o 15.5 17 do do do. 150do 21.2 18 do do do. 185 do 26.1 19 do do do. 225 do 31.8 20 do do do.260 do 36.7 2| do do do. 300 do 42.4

22 5011 I10 250 .75 0885 12.8 31 do. do. y do. 110 do. 18.8 24 do. do.do. 150 do. 2.5.6 2 do. do. do. 185 do. 31.6 20 do. do. do. 225 do. 18.427 do. I do. do. 260 do, 44.4 28 do. do. do. 300 do. 51.2

TABLE IV 1 The data irithe above Tables rv'imd'v show that do creasingthe temperature of the inlet air to the primary SUMMARY OF EMISSION DATAFROM COMBUSTOR A v gcombustion zone decreases the NO, emissions. The

lrimary Zone Emissions, lb./ 1000 lb. fuel l itemperature of the inletair to the second zone of the 5 Ecombustor (inlet at openings 70) wasnot measured but 9 Rwdence Y CO (as approximated the temperature of theprimary air. Thus, Condition Tlme, msec Ratio, dla. NO) C) the data alsoshow that CO emlssions increase with de- Number creasmg mlet airtemperatures to the secondary combustion zone, and decrease withincreasing inlet air 1 L85 193 g 10 temperatures to said secondarycombustion zone. g 3: g; g: 3' The data from the above runs thusillustrate the ad- 4 4 02 vantages of operating a combustor and heatenergy utido. 5.54 2.4 0.2 lization system in accordance with theinvention. By 6 3 9 -28 g g; heat exchanging an exhaust gas stream from,the heat 7 h energy utilization zone (such as turbine exhaust gases) 8 7L34 9 5 51 05 with one or more other air streams to the combustor 9 do.2.72 4 1 .35 1.2 such as the quench air (and also heating the secondary:3 3 2;; 8 32 8g air if desired), instead of the primary air, acombustor [2 z: A 24 1 canbe operated with a low primaryair inlettempera- 13 do. 6.40 0 9 17 0.1 ture, a controlled secondary arr inlettemperature 14 i 2 2 which can be the same as or greater than thetemperature of the inlet primary air, and a heated quench air 15 76.61.85. 5.7 0 0.5 I h h th 16 H0 18 94 0'3 stream w 1c can ave a greatertemperature an e1- 17 do. 3.70 1.4 108 0.2 ther said primary air or saidsecondary air. The method 18 d0. I of the invention thus provides for alow primary inlet :3 g;- 2'23 8'; 2g 8'? air temperature to give low N0,emissions values, a 217 40 j (17 controlled secondary air inlettemperature to give de- 1 s1red CO emissions values, and a heated quenchmlet 22 1- 3- 2 -3 air to conserve heatenergy and incr'easethe overallef- 23 -f1ciency of the system. 24 do. 3.70 1.1 134 0.2 1 25 do, 456 109In'general, said data also show that vN),,, em1ss1 or1s 26 do. 5.54 0.872 decrease with increasing equivalence ratio in the pri- 27 W g: I marycombustion zone (increasing fuelrich mixture), 28 and tend to plateau atlow levels with an increase in heat input. Said equivalence ratio s werecalculated from the percent Total Combustor Hole Area for the TABLE Vair inlet conduits to theprimary combustion zone. The data set forth inthe above Tables IV and V show SUMMARY O EMISSION DATA FROM COMBUSTQR B5 ,that combustors can -be operated in accordance with 40 @the inventionto give low N0 low CO, and low HC emissions when using either aprevaporized fuel or an Test Residence Equivalence NOAaS CO 1 atomizedliquid fuel. Said data also show that the vari- Primary Zone Emissions,lb./ 1000 lb. fuel 33,122? No) C) ous. operating variables or parametersare interrelated. Thus, a change in one variable or parameter may make 24 it desirable to adjust one or more of the other operating 1 44.2 1.0718.8 0 0.5 1 2 do. 1.57 32 03 vanables or parameters in order to obtaindeslrable re- 3 do. 2.14 5.7 14 0 4 gsults with respect to all threepollutants NO CO, and g:- g-g g g'i 'HC (hydrocarbons). 6 1 2 In onepresently preferred method of the invention, 7 1 the primary combustionzone is preferably operated 1 8 443 L06 9.4 4 Q5 @fuel-rich with respectto the primary air admitted 9 do. -5 77 0.3 thereto. Thus, theequivalence ratio in the primary 10 do. 2.14 1.4 53 0.1- U 163 L4 22 0.3combustion zone is preferably greater than stoichio- 12 do. 3.20 1.5 70.2 metric.- In this method of operation, the second zone L .38 2g? 8-?55 (secondary combustion zone) of the combustor is pref- .erablyoperated fuel-lean with respect to any unburned i2 1 F 8-; fuel and airentering said second zone from said pri- 17 3: 122 mary zone, and anyadditional air admitted to said sec- 18 do. 2.63 1.1 76 0.2. end zone.Thus, the equivalence ratio in said second g3 38: 3:28 f3 81% zonepreferably is less than stoichiometric. This 21 do. 4.26 1.2 4 0.0method of operation is preferred when it is desired to 22 442 L07 3'1 10L4 obtain both low NO, and low CO emissions from a 23 57 14 ()5combustor. In general, it is preferred that the transition v24 g 8-;from the fuel-rich condition in the primary combustion g2 2: 33 5: zoneto the fuel-lean condition in the secondary zone 27 do 3.70 1.0 50 0.6be sharp or rapid, e.g., be effected as quickly as possi-.@EWEQQFBLQQPFBQWF? t thasscond 993.9!

15 Combustion zone be operatedfue l-rich as described, it is within thescope of the invention to operate the'primary combustion zone fuel-lean.Thus, it is withinthe scope of the invention to operate the primarycombustion zone with any equivalence ratio which will give the improvedresults of the invention. v

For example, in the practice of the invention as carried out in lowcompression ratio combustors, e.g., compression ratios up to about 5,the equivalence ratio in the primary combustion zone can have any valuesuch that the NO, emissions value in the exhaust gases from thecombustor is not greater than about 5 pounds, preferably not greaterthan about 3.5 pounds, per 1,000 pounds of fuel burned in saidcombustor. Preferably, said equivalence ratio will be at least 1.5, morepreferably at least 3.5, depending upon the other operating variables orparameters, e.g., temperature of the inlet air to theprimarycombustionzone.

It will be understood that said N 0, emission values referred to in thepreceding paragraph can be greater than the values there given whenoperating high performance combustors. For example, combustors such asthe intermediate compression ratio combustors having a compression ratioof about 5 to atmospheres and the high compression ratio combustorshaving a compression ratio of about 15 to about 40 atmospheres usedv injet aircraft and other high performance engines. The NO, emissions fromsuch high performance or high compression ratio combustors willnaturally be higher than the NO, emissions from low compression ratiocombustors. Thus, greatly improved results in reducing N0, emissionsfrom a high performance com bustor can be obtained without necessarilyreducingsaid NO 'emissions to the same levels as would be obtained froma low performance combustor.

As used herein and in the claims, unless otherwisespecified, the termequivalence ratio for a particular zone is defined as the ratio of thefuel flow (fuel avail-5 able) to the fuel requiredfor stoichiometriccombus-j tion with the air available. Stated another way, said;equivalence ratio is the ratio of the actual fuel-air mixture to thestoichiometric fuel-air mixture. For exam-' vention is not limited'toany particular range or value.

for said inlet air temperature. It is within the scope ofl the inventionto use any primary air inlet temperature; which will give the improvedresults of the invention, for example, from ambient or atmospherictemperatures or lower to about l,500 F. or higher. l-low'ever,considering presently available practical materials of construction,about l,200 F. to about l,500 F. is a practical upper limit for saidprimary air inlet temperature in most instances. Considering otherpractical aspects such as not having to cool the compressor dis-? chargestream, about 200 to 400 F. is a practical lower limit for said primaryair inlet temperature in' many instances. However, it is emphasized thatprimary air inlet temperatures lower than 200F. can be used, e.g., inlow compression ratio combustors.

The data in the above examples also show that the .said inlet primaryair.

the combustor is'zsanaary'ad'rhtu's'iibfi a irYcan be 7 an 7 importantoperating variable or parameter, particularly when the lower primary airinlet temperatures are used, and it is desired to obtain low CO emissionvalues as well as low NO, emission values. Said data show that both lowNO, emission values and low CO emission values can be obtained when thetemperature of the inlet air to both the primary combustion zone and thesecond zone of the combustor are at least about 900 F. As thetemperature of the inlet air to said zones decreases, increasinglyimproved (lower) values for NO, emissions are obtained,but it becomesmore difficult to obtain desirably low CO emission values. It ispreferred that the temperature of the inlet air to the primary.combustion zone not be greater than about 700 F.

Thus, in some embodiments of the invention, it is preferred that thetemperature of the secondary air admitted to the second zone of thecombustor be greater than the temperature of the'primary air admitted tothe primary combustion zone. For example, depending combustion zone, itis preferred that the temperature of the inlet secondary air be in therange of from about to about 500 F. greater than the temperature of As aguide to those construed as necessarily limiting on the invention, the'presently preferred operating ranges for other variables or parametersarerheat input, from 30m 500 Btu per lb. of total air to the combustor;combustor pressure, from 3 to 10 atmospheres; and reference airvelocity, from 50 to 250 feet per second. v Reference has been madeherein to vehicle emission standards which have been set by the UnitedStates En-- vironmental Protective Agency for 19751976. These standardsor goals have been related to gas turbine engine combustors, by assuming10.0 miles per gallon fuel economy and 6.352 pounds per gallon JP-4fuel, as follows:-

Emission Level Criteria EPA Vehicle Gas Turbine Engine Particulates Thedata set forth in the above examples show that' the invention can bepracticed to give pollutant emission levels meeting tha above standardsor goals. Ho'wlever, the invention is not limited to meeting said stan-,dards or goals. Many persons skilled in the art consider esaid standardsor goals to be unduly restrictive. It is {possible that said standardsor goals may be relaxed. Thus, a combustor, and/or. a method ofoperating acombustor, to obtain reduced levels of pollutant emissionsapproaching said standards or goals has greatpo .tential value. While itis not to be considered as limiting upon the temperature of the inletair to the primary Skaters." Haiti "Barnard a :on the invention, it isbelieved that practical maximumsfor low compression ratio gas turbineengine goals.

I would be in the order of, in lbs. per 1,000 lbs. of fuel} to valuesofnot more t han about 2 5,pr'eferably not more than about 1.8, poundsper 1,000 pounds of fuel burned at idle conditions; and not more thanabout 5, preferably not more than about 3.5, pounds per 1,000 pounds offuel burned at maximum power conditions, the invention is not limited tosaid values.

Thus, while certain embodiments of the invention have been described forillustrative purposes, the invention is not limited thereto. Variousother modifica tions or embodiments of the invention'will be apparent:to those skilled in the art in view of this disclosure, Suchmodifications or embodiments are within the spirit and scope of thedisclosure.

1 claim:

1. In a method wherein a stream of air and a stream. of fuel are passedto a combustion zonecomprising a; primary combustion region, a secondarycombustiong region located downstream from said primary combus-l tionregion, and a quench region located downstream; from saidsecondarycombustion region, said fuel and said air are at leastpartially mixed to form a combustiblemixture which is burned to producehot combustionf gases containing heat energy, and said hot combustion;

gases are passed to a heat energy utilization zone to uti-g lize aportion of said heat energy, the improvement; comprising:

dividing said stream of air into a and'a second stream of air;- furtherdividing said first stream of air into a stream comprising primary airand another stream comprising secondaryair; introducing a stream of saidfuel into-said primary combustion region; V introducing said streamcomprising primary air into s i ar as?!.sem ii nrasiaaa burning saidfuel; introducing said stream comprising secondary air into saidsecondary combustion region at a temperature within the range of fromabout 100 to about 500 F. greater than the temperature of said primaryair;

first stream of airpassing said second stream of air in heat exchangerelationship with an exhaust stream from said heat energy utilizationzone to heat said second stream of air and thereby utilize an additionalportion of said energy; and

passing at least a portion of said heated second stream of air into saidquench region of said combustion zone.

2. A method according to claim 1 wherein the temperature of said primaryair is not greater than about 700 F.

3. A method according to claim 2 wherein the equivalence ratio in saidprimary combustion region is greater than stoichiometric and is adjustedto a value such that the N01, emissions value in the exhaust gases fromsaid combustion zone is not greater than about pounds per 1,000 poundsof fuel burned in said combustion zone.

4. A method according to claim 3 wherein the CO emissions value in theexhaust gases from said combustion zone is not greater than about 25pounds per 1,000 pounds of fuel burned in said combustion zone.

5. A method according to claim 4 wherein the equivalence ratio in saidprimary combustion region is at 9aa-- ...W

6. A method for forming and burning a combustible mixture of a fuel andair in a combustion zone having a primary combustion region, a secondarycombustion region located downstream from said primary combus tionregion, and a quench region located downstream from said secondarycombustion region, to produce hot combustion gases containing heatenergy which are passed to a heat energy utilization zoneto utilize aportion of said heat energy, which method comprises:

dividing a stream of air into a first stream of air and a'second streamof air; further dividing said first stream of air into a Streamcomprising primary combustion air and another stream comprisingsecondary combustion air; introducing a stream of fuel into said primarycombustion region; introducing said stream comprising primary combustionair into said primary combustion region at a temperature not greaterthan about 700 F.;

burning said fuel; v

introducing said stream comprising secondary combustion air into saidsecondary region at a temperature within the range of from about toabout 500 F. greater than the temperature of said primary air; passingsaid second stream of air in heat exchange relationship with an exhauststream from said heat energy utilization zone to heat said second streamof air; and introducing at least a portion of said heated second streamof air into said quench region of said combustion zone. 1

7. A method for forming and .buming a combustible mixture of a fuel andairin a combustion zone having a primary combustion region, a secondarycombustion region located downstream from said primary combustionregion, and a quench region located downstream from said secondarycombustion region, to produce hot combustion gases containing heatenergy which are lpassed to a heat energy utilization zone to utilize aportion of said heat energy, which method comprises:

dividing a stream of air into a first stream of air and a second streamof air; further dividing said first stream of air into a streamcomprising primary combustion air and another stream comprisingsecondary combustion air; introducing a stream of fuel into said primarycombustion region; introducing said stream comprising primary combustionair into said primary combustion region at a temperature not greaterthan about 700 F. and inan amount relative to said fuel sufficient toprovide a fuel-rich mixture having an equivalence ratio in said primarycombustion region greater than stoichiometric; burning said fuel;

introducing said stream comprising secondary compassing said secondstream of air in heat exchange re- 19 energy utilization zone to heatsaid second stream of air; and introducing at least a portion of saidheated second stream of air into said quench region of said combustionzone at a temperature greater than the temperature of said secondaryair. 1

8. A method according to claim 7 wherein said stream of air comprisingprimary combustion air is not more than about 25 percent of the totalair introduced into said combustion zone.

9. A method according to claim 8 wherein said stream of air comprisingprimary combustion air is not more than about 5.6 percent of the totalair introduced into said combustion zone.

10. A method according to claim 7 wherein said equivalence ratio isadjusted to a value such that the NO, emissions value inthe exhaustgases from said combustion zone is not greater than about pounds perl,000 pounds of fuel burned in said combustion zone. 11. A methodaccording to claim 10 wherein said equivalence ratio is at least about1.5.

12. A method according to claim l0'wherein said;

equivalence ratio is at least about 3.5.

13. A method'according to claim 7 wherein the greater thanstoichiometric and is adjusted to a value equivalence ratio in saidprimary combustion region is 15. A method according to claim 14 whereinsaid equivalence ratio is at least about 1.5.

16. A method according to claim 14 wherein saidequivalence ratio is atleast about 3.5.

17. A method for forming and burning a combustible mixture of a fuel andair in a combustion zone having' a primary combustion region, asecondary combustion region located downstream from said primarycombustion region, and a quench region located downstream from saidsecondary combustion region, to produce hot combustion gases containingheat energy which are passed to a heat energy utilization zone toutilize a portion of said heat energy, which method comprises:

dividing .a stream of air into a first stream of air and a second streamof air; further dividing said first stream of air into a streamcomprising primary combustion air and another stream comprisingsecondary combustion air; introducing a stream of fuel into said primarycombustion region; introducing said stream comprising primary combustionair into said primary combustion region; burning said fuel; introducingsaid stream comprising secondary combustion air into said secondaryregion at a temperature at least 100 F. greater than the temperaturestream of air into said quench region of said combustion zone. I

18. A method according to claim 17 wherein said heated second stream ofair is passed in heat exchange with an outer wall of said primarycombustion region so as to remove heat from the interior of said primarycombustion region and further heat said air, and is then introduced intosaid quench region.

19. A method according to claim 17 wherein:

1 said heated second stream of air is passed in a first annular streamsurrounding an outer wall of said primary-combustion region and aportion of said secondary combustion region, and is then introduced intosaid quench region; and

said secondary air is passed in a second annular stream surrounding butseparated from said first annular stream, and is then introduced intosaid secondary combustion region.

20. A method according to claim 17 wherein the tem- 21. A methodaccording to claim 17 wherein a portion of said heated second stream ofair is mixed with said secondary air-so as to increase the temperatureof said secondary air.

22. A method for forming and burning a combustible mixture of a fuel andair in a combustion zone having a primary combustion region, a secondarycombustion region located downstream from said primary combustionregion, and a quench region located downstream from said secondarycombustion region, to produce hot combustion gases containing heatenergy which are passed to a heat energy utilization zone to utilize aportion of said heat energy, which method comprises:

dividing a stream of air into a first stream of air and z. second s ea fa further dividing said first stream of air into a stream comprisingprimary combustion air and another stream comprising secondarycombustion air; introducing a stream of fuel into said primarycombustion region; introducing said stream comprising primary combustionair into said primary combustion region in an amount relative to saidfuel sufficient to provide a fuel-rich mixture having an equivalenceratio in said primary combustion region greater than stoichiometric;burning said fuel; introducing said stream comprising secondarycombustion air into said secondary region, in an amount sufficient toprovide a fuel-lean mixture in said secondary region with respect to anyunburned fuel entering said secondary region from said primary region,and at a temperature at least F. greater than the temperature of saidintroduced primary air;

passing said second stream of air in heat exchange relationship with anexhaust stream from said heat energy utilization zone to heat saidsecond stream of air; and

introducing at least a portion of said heated second stream of air intosaid quench region of said combustion zone at a temperature greater thanthe temperature of said secondary air.

1. In a method wherein a stream of air and a stream of fuel are passedto a combustion zone comprising a primary combustion region, a secondarycombustion region located downstream from said primary combustionregion, and a quench region located downstream from said secondarycombustion region, said fuel and said air are at least partially mixedto form a combustible mixture which is burned to produce hot combustiongases containing heat energy, and said hot combustion gases are passedto a heat energy utilization zone to utilize a portion of said heatenergy, the improvement comprising: dividing said stream of air into afirst stream of air and a second stream of air; further dividing saidfirst stream of air into a stream comprising primary air and anotherstream comprising secondary air; introducing a stream of said fuel intosaid primary combustion region; introducing said stream comprisingprimary air into said primary combustion region; burning said fuel;introducing said stream comprising secondary air into said secondarycombustion region at a temperature within the range of from about 100*to about 500* F. greater than the temperature of said primary air;passing said second stream of air in heat exchange relationship with anexhaust stream from said heat energy utilization zone to heat saidsecond stream of air and thereby utilize an additional portion of saidenergy; and passing at least a portion of said heated second stream ofair into said quench region of said combustion zone.
 2. A methodaccording to claim 1 wherein the temperature of said primary air is notgreater than about 700* F.
 3. A method according to claim 2 wherein theequivalence ratio in said primary combustion region is greater thanstoichiometric and is adjusted to a value such that the NOx emissionsvalue in the exhaust gases from said combustion zone is not greater thanabout 5 pounds per 1,000 pounds of fuel burned in said combustion zone.4. A method according to claim 3 wherein the CO emissions value in theexhaust gases from said combustion zone is not greater than about 25pounds per 1,000 pounds of fuel burned in said combustion zone.
 5. Amethod according to claim 4 wherein the equivalence ratio in saidprimary combustion region is at least about 3.5.
 6. A method for formingand burning a combustible mixture of a fuel and air in a combustion zonehaving a primary combustion region, a secondary combustion regionlocated downstream from said primary combustion region, and a quenchregion located downstream from said secondary combustion region, toproduce hot combustion gases containing heat energy which are passed toa heat energy utilization zone to utilize a portion of said heat energy,which method comprises: dividing a stream of air into a first stream ofair and a second stream of air; further dividing said first stream ofair into a stream comprising primary combustion air and another streamcomprising secondary combustion air; introducing a stream of fuel intosaid primary combustion region; introducing said stream comprisingprimary combustion air into said primary combustion region at atemperature not greater than about 700* F.; burning said fuel;introducing said stream comprising secondary combustion air into saidsecondary region at a temperature within the range of from about 100* toabout 500* F. greater than the temperature of said primary air; passingsaid second stream of air in heat exchange relationship with an exhauststream from said heat energy utilization zone to heat said second streamof air; and introducing at least a portion of said heated second streamof air into said quench region of said combustion zone.
 7. A method forforming and burning a combustible mixture of a fuel and air in acombustion zone having a primary combustion region, a secondarycombustion region located downstream from said primary combustionregion, and a quench region located downstream from said secondarycombustion region, to produce hot combustion gases containing heatenergy which are passed to a heat energy utilization zone to utilize aportion of said heat energy, which method comprises: dividing a streamof air into a first stream oF air and a second stream of air; furtherdividing said first stream of air into a stream comprising primarycombustion air and another stream comprising secondary combustion air;introducing a stream of fuel into said primary combustion region;introducing said stream comprising primary combustion air into saidprimary combustion region at a temperature not greater than about 700*F. and in an amount relative to said fuel sufficient to provide afuel-rich mixture having an equivalence ratio in said primary combustionregion greater than stoichiometric; burning said fuel; introducing saidstream comprising secondary combustion air into said secondary region,in an amount sufficient to provide a fuel-lean mixture in said secondaryregion with respect to any unburned fuel entering said secondary regionfrom said primary region, and at a temperature within the range of fromabout 100* to about 500* F. greater than the temperature of saidintroduced primary air; passing said second stream of air in heatexchange relationship with an exhaust stream from said heat energyutilization zone to heat said second stream of air; and introducing atleast a portion of said heated second stream of air into said quenchregion of said combustion zone at a temperature greater than thetemperature of said secondary air.
 8. A method according to claim 7wherein said stream of air comprising primary combustion air is not morethan about 25 percent of the total air introduced into said combustionzone.
 9. A method according to claim 8 wherein said stream of aircomprising primary combustion air is not more than about 5.6 percent ofthe total air introduced into said combustion zone.
 10. A methodaccording to claim 7 wherein said equivalence ratio is adjusted to avalue such that the NOx emissions value in the exhaust gases from saidcombustion zone is not greater than about 5 pounds per 1,000 pounds offuel burned in said combustion zone.
 11. A method according to claim 10wherein said equivalence ratio is at least about 1.5.
 12. A methodaccording to claim 10 wherein said equivalence ratio is at least about3.5.
 13. A method according to claim 7 wherein the equivalence ratio insaid primary combustion region is greater than stoichiometric and isadjusted to a value such that the NOx emissions value in the exhaustgases from said combustion zone is not greater than about 5 pounds per1,000 pounds of fuel burned in said combustion zone.
 14. A methodaccording to claim 13 wherein the CO emissions value in the exhaustgases from said combustion zone is not greater than about 25 pounds per1,000 pounds of fuel burned in said combustion zone.
 15. A methodaccording to claim 14 wherein said equivalence ratio is at least about1.5.
 16. A method according to claim 14 wherein said equivalence ratiois at least about 3.5.
 17. A method for forming and burning acombustible mixture of a fuel and air in a combustion zone having aprimary combustion region, a secondary combustion region locateddownstream from said primary combustion region, and a quench regionlocated downstream from said secondary combustion region, to produce hotcombustion gases containing heat energy which are passed to a heatenergy utilization zone to utilize a portion of said heat energy, whichmethod comprises: dividing a stream of air into a first stream of airand a second stream of air; further dividing said first stream of airinto a stream comprising primary combustion air and another streamcomprising secondary combustion air; introducing a stream of fuel intosaid primary combustion region; introducing said stream comprisingprimary combustion air into said primary combustion region; burning saidfuel; introducing said stream comprising secondary combustion air intosaid secondary region at a temperature at least 100* F. greater than thetemperature of said primary combustion air; passing said second streamof air in heat exchange relationship with an exhaust stream from saidheat energy utilization zone to heat said second stream of air; andintroducing at least a portion of said heated second stream of air intosaid quench region of said combustion zone.
 18. A method according toclaim 17 wherein said heated second stream of air is passed in heatexchange with an outer wall of said primary combustion region so as toremove heat from the interior of said primary combustion region andfurther heat said air, and is then introduced into said quench region.19. A method according to claim 17 wherein: said heated second stream ofair is passed in a first annular stream surrounding an outer wall ofsaid primary combustion region and a portion of said secondarycombustion region, and is then introduced into said quench region; andsaid secondary air is passed in a second annular stream surrounding butseparated from said first annular stream, and is then introduced intosaid secondary combustion region.
 20. A method according to claim 17wherein the temperature of said first stream of air is not greater thanabout 700* F.
 21. A method according to claim 17 wherein a portion ofsaid heated second stream of air is mixed with said secondary air so asto increase the temperature of said secondary air.
 22. A method forforming and burning a combustible mixture of a fuel and air in acombustion zone having a primary combustion region, a secondarycombustion region located downstream from said primary combustionregion, and a quench region located downstream from said secondarycombustion region, to produce hot combustion gases containing heatenergy which are passed to a heat energy utilization zone to utilize aportion of said heat energy, which method comprises: dividing a streamof air into a first stream of air and a second stream of air; furtherdividing said first stream of air into a stream comprising primarycombustion air and another stream comprising secondary combustion air;introducing a stream of fuel into said primary combustion region;introducing said stream comprising primary combustion air into saidprimary combustion region in an amount relative to said fuel sufficientto provide a fuel-rich mixture having an equivalence ratio in saidprimary combustion region greater than stoichiometric; burning saidfuel; introducing said stream comprising secondary combustion air intosaid secondary region, in an amount sufficient to provide a fuel-leanmixture in said secondary region with respect to any unburned fuelentering said secondary region from said primary region, and at atemperature at least 100* F. greater than the temperature of saidintroduced primary air; passing said second stream of air in heatexchange relationship with an exhaust stream from said heat energyutilization zone to heat said second stream of air; and introducing atleast a portion of said heated second stream of air into said quenchregion of said combustion zone at a temperature greater than thetemperature of said secondary air.